1. Field of the Invention
The present invention relates to a ceramic electronic component and a method for manufacturing the same, and more particularly, to external electrodes of a ceramic electronic component and a method for forming the external electrodes by an electrolytic plating method.
2. Description of the Related Art
A related multilayer ceramic capacitor includes a laminate which includes dielectric ceramic layers laminated to each other and layered internal electrodes provided along interfaces therebetween and external electrodes provided on the laminate so as to electrically connect the internal electrodes which are exposed on surfaces of the laminate. An example of this related multilayer ceramic capacitor is shown in FIG. 3.
As shown in FIG. 3, external electrodes are provided on surfaces of a laminate 102 at which internal electrodes 104 and internal electrodes 105 are exposed so as to electrically connect the respective internal electrodes 104 and 105. In a typical method for forming external electrodes, a metal paste including a metal component and a glass component is applied to the surfaces at which the internal electrodes are exposed and is then fired by a heat treatment, such that paste electrode layers 106 and 107 are formed.
Subsequently, first plating layers 108 and 109 primarily including Ni are formed on surfaces of the paste electrode layers 106 and 107, respectively, and second plating layers 110 and 111 primarily including Sn are formed on surfaces of the first plating layers 108 and 109, respectively. That is, the external electrodes each have a three-layer structure including the paste electrode layer, the first plating layer, and the second plating layer.
The external electrodes are required to have high wettability to solder when a multilayer ceramic capacitor is mounted on a substrate using solder. At the same time, the external electrodes must function to electrically connect the internal electrodes which are electrically insulated from each other. The second plating layers 110 and 111 primarily including Sn ensure the solder wettability, and the paste electrode layers 106 and 107 electrically connect the internal electrodes. The first plating layers 108 and 109 function as underlying layers for the second plating layers 110 and 111, respectively, in order to prevent solder leaching during solder mounting.
However, each of the paste electrode layers 106 and 107 has a relatively large thickness of approximately several tens to several hundreds of micrometers. Thus, when this multilayer ceramic capacitor is formed so that the dimensions thereof conform to a predetermined standard value, an effective volume to ensure electrostatic capacitance must be decreased in an amount corresponding to the volume required to form the paste electrode layers. On the other hand, since the plating layers each have a thickness of approximately several micrometers, if the external electrodes can be formed only from the first and the second plating layers, a greater effective volume can be ensured.
For example, a method is disclosed in Japanese Unexamined Patent Application Publication No. 63-169014 in which conductive metal layers are deposited by electroless plating over substantially the entire side wall surfaces of a laminate at which internal electrodes are exposed so as to short-circuit the respective internal electrodes exposed at the side wall surfaces. However, with this method, a bonding force of the conductive metal layer formed by electroless plating to the side wall surface is weak, and reduced reliability may occur.
In addition, in Japanese Unexamined Patent Application Publication No. 5-343259, a technique is disclosed in which external electrodes having superior adhesion are formed by forming electroless plating films including glass powder dispersed therein on bare ceramic surfaces.
However, with the method for forming external electrodes disclosed in Japanese Unexamined Patent Application Publication No. 5-343259, since the plating method is electroless plating, depending on subsequent heat treatment conditions, blisters are likely to be generated in the electroless plating film. When blisters are generated, moisture may enter therethrough, and problems, such as degradation in reliability, may arise.
Furthermore, with the above-described method for forming external electrodes, since the plating method is electroless plating, if it is attempted to co-deposit glass powder together with metal ions, there is a problem in that the glass is dissolved or is not sufficiently deposited.